Sensors are used to sense a variety of different quantities. For example, the quantity or parameter to be sensed can be a magnetic field, a current, a temperature, a pressure or a position. Commonly used sensing structures include piezoelectric elements positioned on or formed in a flexible diaphragm for sensing pressure, electrically conducting or semiconducting elements based on the Hall effect, magnetoresistance or variable reluctance structures for sensing magnetic fields.
Hall sensors are one form of magnetic field sensor that can be manufactured at low cost particularly when embodied as an integrated (monolithic) sensor. When a current-carrying conductor or semiconducting Hall element is placed into a magnetic field, a voltage will be generated orthogonal to the direction of both the current and the magnetic field. This principle is known as the Hall effect.
The Hall element is generally constructed from a thin sheet of conductive or semiconducting material with output connections perpendicular to the direction of current flow. When subjected to a magnetic field, the Hall element responds with an output voltage proportional to the magnetic flux density. The output voltage is generally very small (on the order of several μV) and thus requires electronics to provide gain to achieve useful signal levels. When the Hall element is combined with the associated signal processing sensor electronics, it forms a Hall effect sensor. Integrated Hall effect sensors comprise an integrated circuit chip (e.g. silicon) that contains the Hall element and the signal conditioning electronics.
Analog sensors provide an analog output voltage which is proportional to the magnitude of the magnetic field input (sensed). Conventional digital output Hall sensors use a Schmitt trigger or other hysteresis-generating circuitry to convert the basic analog output sensor to a digital output sensor. The output of a digital sensor is one of two binary levels, 1 or 0 (ON or OFF). The Schmitt trigger or other equivalent hysteresis-generating circuit is operable to convert the analog output of the amplifier, that is coupled to the Hall elements, into a binary output level, 1 or 0 (ON or OFF) and to provide a reasonable noise margin between the sensed binary states.
Supply voltage rejection and temperature compensation are important performance characteristics for sensors such as integrated Hall sensors. For example, digital output Hall sensors require these characteristics to control the amount of change in the magnetic transition points, that define the binary output states, over operating ranges of both supply voltage and temperature.
A common technique for obtaining supply voltage rejection is to include a voltage regulator to provide a stable bias for the Hall element and the signal processing circuitry. It is also desirable for the regulated voltage provided by the voltage regulator to be nearly constant over temperature, to provide a reference for temperature compensation. The trade-offs in using precision on-chip voltage regulation is larger die size/cost and additional supply current. Driven primarily by commercial Hall market pricing, specifications and die size constraints imposed by contemporary surface mount packages, a need exists for having a small die size that operates at lower power and also provides competitive magnetic specifications.